JPH03121773A - Polishing method for high flatness of silicon wafer - Google Patents

Abstract

PURPOSE:To obtain a wafer of good flatness in <=2mum, by polishing a Si wafer with the rocking speed of 1/4 circle of a surface plate being controlled in 3-6 and the rocking speed of the surface plate outer peripheral part in 1.5-3, provided the rocking speed of the surface plate center part is taken as 1. CONSTITUTION:A Si wafer 5 is polished by its rocking, while controlling the rocking speed of a surface plate 1 outer peripheral part in 1.5-3 and that of 1/4 circle of the surface plate 1 in 3-6, provided the rocking speed of the stoppage position 2 of the surface plate 1 center side is taken in 1. In this case, this rocking pattern coincides with the ear curve of an abrasive cloth of the polishing time with the rocking speed of the Si wafer being made constant and the Si wafer 5 is polished in the flatness of <=2mum.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a method for polishing (also referred to as mirror polishing) a Si wafer.

Conventional technology Conventionally, in polishing (mirror finishing) of Si wafers, the second
As shown in the figure, the Si wafer 5 is pressed against the polishing cloth 4 stuck on the surface plate L, and the center of the Si wafer is moved back and forth between the surface plate center side stop position 2 and the surface plate outer peripheral side stop position 3. (hereinafter referred to as oscillation). At this time, an overlap amount of 6 (diameter of the Si wafer diameter!0%) is taken and polished. Moreover, as shown in FIG. 3, the rocking speed is constant at any position in the radial direction of the surface plate. This causes the following problems.

Due to contact with the polishing cloth 4, after polishing for 30 minutes, the Si wafer 5 wears 2 lm at the stop position M2 on the center side of the surface plate, and wears 4 lm at the stop position 3 on the outer peripheral side of the surface plate, as shown in FIG. There is wear of 6 rivers m at the position of circle A. In this way, the wear of the polishing cloth is not constant in the radial direction of the surface plate. This phenomenon is called uneven wear. Due to this uneven wear of the polishing cloth 4, the surface shape of the Si wafer is centered as shown in FIG. The current situation is that it has become 2 gm higher and cannot become any more flat.

Problems to be Solved by the Invention In view of the above-mentioned problems, an object of the present invention is to provide a method for polishing a Si wafer to a high degree of flatness.

Means for Solving the Problems The present invention provides a method for polishing (mirroring) a Si wafer, in which when the rocking speed of the Si wafer at the stop position on the center side of the surface plate is 1, the rocking speed of the outer peripheral part of the surface plate is 1.5-3
, and is characterized in that polishing is performed by rocking the surface plate while controlling the rocking speed of 3 to 6% circles.

Furthermore, the present invention is characterized in that the rocking speed is controlled in accordance with the wear curve of the polishing cloth when polishing is performed while keeping the rocking speed of the Si wafer constant.

Function The present invention will be explained in detail below. What is policing?
A monocrystalline plate (Si wafer) on a disk with a diameter of 5 to 1 oin cut thinly (approximately 0.7 mm) from a monocrystalline Si ingot is fixed on a surface plate l as shown in Figure 6. Abrasive grains 14 (for example, 5i
02 with an average particle diameter of 0.02 gm) is supplied between the polishing cloth 4 and the Si wafer, and a load of 12 (for example, 250 g/cm2 in surface pressure on the wafer surface) is applied to the Si wafer 5.
), and a relative velocity of 1 is applied to the surface plate l and the Si wafer 5.
5 (for example, 3 m/5 inch), and the Si wafer 5 is brought into contact with the abrasive grains 14.
This process involves processing the material into a flat, mirror-like surface.

The present invention provides a method for polishing a Si wafer 5 extremely flat. To this end, the key point of the present invention is to control the swinging speed so as not to wear the polishing cloth unevenly. The rocking speed was determined as follows.

In other words, as shown in Fig. 4, from the measurement results of the wear curve when the rocking speed is kept constant, when the rocking speed is slow, it is because the Si wafer is in contact with one point of the polishing cloth for a long time. ,
Focusing on the progress of wear, the rocking speed of the Si wafer is slow near the stop position 2 on the center side of the surface plate, and the rocking speed near the stop position 3 on the outer peripheral side of the surface plate is lower than that near the stop position 2 on the center side of the surface plate. It has been found that it is effective to perform polishing by swinging the surface plate faster than the swinging speed, and faster than the swinging speed of the h-circle of the surface plate near the stop position 3 on the outer circumferential side of the surface plate while controlling the speed. Ta.

FIG. 1 shows the relationship between the swing position and swing speed of St. The rocking speed near the stop position 2 on the center side of the surface plate is 5 cm/S, the rocking speed near the stop position 3 on the outer periphery of the surface plate is 10 c/S, and the rocking speed of the % circle of the surface plate is 20 cm/S. The speed pattern is made to approximately match the shape of the abrasive cloth wear curve shown in FIG.

When the Si wafer was polished by controlling the rocking speed in this way, the flatness of the Si wafer was 0.51L as shown in Figure 9.
m was obtained. From the experimental results, if the rocking speed near the stop position 2 on the center side of the surface plate is 1, the rocking speed near the stop position 3 on the outer peripheral side of the surface plate is 1.5 to 3, and the rocking speed of the ζ circle of the surface plate is 3~
It was found that 6 is preferable.

However, since the wear curve of the polishing cloth 4 differs depending on other polishing conditions (for example, the rotation speed of the surface plate, the type of polishing cloth, etc.), it is easy and reliable to match the rocking speed to the wear curve as described above. This is a great method. Although the swinging speed near the stop position 2 on the center side of the surface plate is 5 cm's in FIG. 1, a faster speed is also possible. However, when the speed exceeds 100 cm/s, S
The followability of the universal joint that supports the i-wafer deteriorates, making it impossible to obtain a flatness of less than 2JLm for the Si wafer.However, numerical control of the speed can be easily achieved by connecting a commercially available personal computer to a polishing machine.

EXAMPLE Below, the present invention will be described in detail.A surface plate with a radius of 300 square meters has a load of 2E! Og/c■2, processing fluid KO)l (p
H11), a 6-inch wafer was polished using 5i02 abrasive grains. When polishing was performed for 80 minutes using the speed control pattern shown in FIG. 7, a flatness of 0.41 Lm was obtained.

In another example, a surface plate with a radius of 300 layers has a load of 2.
00g/cm 2. A 6-inch wafer was polished using a processing liquid KOH (pH 11.5) and 5i02 abrasive grains. After polishing for 80 minutes using the speed control pattern shown in Figure 8,
Flatness of 0.5 p, m was obtained.

Effects of the Invention As a result of the present invention, a wafer with a good flatness of 2JLm or less was produced, and a technology capable of producing ICs compatible with a high degree of integration of 18M or more was established.

[Brief explanation of drawings]

Fig. 1 is a diagram of the swing control pattern according to the present invention, Fig. 2 is a diagram showing the positional relationship between the rocking of the surface plate and the Si wafer used in the present invention, and Fig. 3 is a diagram showing the swing control pattern of the Si wafer at a constant speed. Fig. 4 is a diagram showing the wear curve of the polishing cloth, Fig. 5 is an explanatory diagram of the case of S
Figure 6 shows the i-wafer flatness curve, Figure 6 is an explanatory diagram of Si wafer polishing, Figures 7 and 8 are diagrams showing examples of rocking speed control patterns, and Figure 9 shows the flatness of the Si wafer. It is an explanatory diagram. 1... Surface plate, 2... Surface plate center side stop position, 3...
Stop position on the outer circumference of the surface plate, 4... Polishing cloth, 5... Si wafer, 6... O overlap amount, 7... Center of the surface plate,
8... Inner circumference of the surface plate, 9φ... Outer circumference of the surface plate, V... Oscillation speed.

Claims (2)

[Claims] (1) In a method of polishing (mirror finishing) by moving the Si wafer back and forth between the center and the outer periphery of the surface plate (hereinafter referred to as rocking), the Si wafer is moved at a rocking speed of 1 at the center of the surface plate.
High flatness of a Si wafer characterized by controlling the rocking speed of the quarter circle of the surface plate to 3 to 6 and the rocking speed of the outer periphery of the surface plate to 1.5 to 3. Degree polishing method. (2) In a method of polishing (mirror finishing) by moving the Si wafer back and forth between the center and the outer periphery of a surface plate, the polishing cloth is matched to the wear curve when polishing is performed with the Si wafer rocking at a constant speed. A high flatness polishing method for Si wafers characterized by polishing by controlling the rocking speed.